Contrast-enhanced ultrasound plays an increasingly important role in the characterization of tumors of various organs. In contrast-enhanced ultrasound imaging, the ultrasound data of an imaging region corresponding to a target organ or location of a body is continuously acquired when contrast agent washes into and out of the imaging region. In order to have quantitative measures for the wash-in and wash-out process of the contrast agent, a time-intensity curve that represents the contrast intensity as a function of time is often derived from the ultrasound data and various perfusion parameters may be further derived from the time-intensity curve. Typical perfusion parameters include: area under the curve parameter, peak intensity parameter, time to peak parameter, wash-in time parameter, wash-out time parameter, wash-in rate parameter, wash-out rate parameter, arrival time parameter, mean transit time parameter, rising time parameter, etc.
International patent application WO2009093211A1 (Michalakis et al.) describes that it is desirable that such quantitative measures be repeatable and immune to variations from one imaging procedure to the next, such as variation of the contrast agent injection, patient cardiac output, and ultrasound machine settings which may differ from one examination day to another, and it is proposed to manually identify a region of normal tissue and then compute a wash-in parameter ratio of a region of interest, such as a tumor region, as a ratio of the wash-in parameter of the region of interest and the wash-in parameter of the region of normal tissue. The effects of the aforementioned variations on the wash-in parameter of the region of interest are reduced by dividing it by a reference wash-in parameter, i.e. the wash-in parameter of normal tissue.
However, since different operators may identify different regions as the region of normal tissue, and even the same operator may identify different regions as the region of normal tissue in different imaging procedures, the computed wash-in parameter ratio is dependent on operators' manual manipulations.
US 2005/065432 A1 discloses a blood-flow analysis apparatus for analyzing the time intensity curve for each pixel of region of interest of time-series images collected by photographing a desired region of a sample over time with a mechanical modality by applying a tracer to the blood of the sample. The analysis apparatus includes a calculation unit for calculating parameters indicative of blood-flow dynamics peculiar to the measured tissue of the sample as a ratio to or difference from parameters at a desired reference region on the basis of only the time intensity curve of the measured tissue, and a visual-information presentation unit for visually presenting the calculations by the calculation unit.